The present invention relates to a vehicle axle crosspiece of the kind which includes a first tube, one end of which is fixed to a wheel arm situated on one side of the vehicle, and the other end of which is directed toward another wheel arm situated on the other side of the vehicle, and a second tube engaged partially inside the first tube and fixed at its outer end to the other wheel arm, the inner tube and the outer tube being joined together by at least two antiroll articulations made of elastomeric material, spaced apart in the longitudinal direction of the tubes and housed between the outside surface of the inner tube and the inside surface of the outer tube, each antiroll articulation having its own radial stiffness.
Such an axle crosspiece may be mounted either along the axis of articulation of the arms to the body of the vehicle or, alternatively, parallel to such axis, offset toward the wheels. This crosspiece improves the antiroll behavior of the wheel set concerned.
Each antiroll articulation may have a stiffness which differs in the radial direction; for example, the stiffness may be different in a direction which is vertical, horizontal or at 45xc2x0. To achieve that, an asymmetric antiroll articulation or one which has cavities in a determined distribution in the various directions may be provided. It is thus possible to best compensate for the deformation loadings which differ in the radial directions. Of course, it is also possible to use antiroll articulations the radial stiffness of which remains constant regardless of the radial direction.
Such a crosspiece poses a problem regarding the behavior of the vehicle, particularly in a bend, as a result of the flexural deformations of the axle crosspiece. This is because the two tubes of the crosspiece, which have different diameters, have different inertias. With a crosspiece according to the state of the art, the flexural deformations of the crosspiece depend substantially on the direction of the bend which means that the behavior of the vehicle changes according to whether the bend is to the left or to the right.
It is an object of the invention to provide an axle crosspiece of the foregoing type, which has substantially the same flexural deformations, at least for one considered radial direction, whatever the direction of the bend. In other words, the invention aims to provide an axle crosspiece which has flexural symmetry. It is also desirable for the crosspiece to remain simple in construction and of an acceptable cost price.
According to the invention, a vehicle axle crosspiece of the kind defined previously is characterized in that the antiroll articulations, each assigned a coefficient proportional to its radial stiffness, have a center of inertia which is closer to the wheel arm connected to the outer tube of the crosspiece than to the other wheel arm.
The contribution that the antiroll articulations make to the bending of the crosspiece may be likened to an xe2x80x9celastic pivotxe2x80x9d situated at their center of inertia, having a flexural rigidity which depends on the radial stiffnesses of the articulations and on their spacing. The solution of the invention, by offsetting this center of inertia toward the side of the wheel arm connected to the more rigid outer tube, makes it possible to make the contribution of the pivot more appreciable on the side of such wheel arm, thus compensating for the difference in rigidity of the tubes and contributing to the symmetry of the flexural deformations of the crosspiece.
Advantageously, such offsetting of the center of inertia is obtained in part by the use of articulations which have different radial stiffnesses, the articulation closest to the wheel arm connected to the outer tube having the higher radial stiffness.
As a preference, the radial stiffness of the antiroll articulation closest to the wheel arm connected to the outer tube is at least 20%, and, more preferably still, at least 35%, greater than the radial stiffness of the other articulation.
Advantageously, the geometric center of the antiroll articulations is offset to the side of the arm connected to the outer tube, that is to say, closer to this arm than to the other arm. In particular, if L denotes the length of the crosspiece, the distance from the geometric center of the antiroll articulations to the arm connected to the outer tube is less than 0.45 L.
According to another aspect of the invention, which may be considered alone or in combination with the previous one, it is desirable to optimize the overall rigidity of the crosspiece. In particular, it is desirable to provide an axle crosspiece with antiroll elastic articulations which has good flexural rigidity without this in any way appreciably modifying the torsional behavior. It is furthermore desirable that the means of obtaining this result remain simple and economical.
According to this other aspect, the distance between the antiroll articulations of the axle crosspiece is chosen so as to optimize the flexural rigidity of the crosspiece as a function of the rigidities of the tubes and of the stiffnesses of the articulations.
Advantageously, the distance between the articulations is between pL and qL, L being the length of the crosspiece and p and q being coefficients equal to 0.3 and 0.6 respectively.
The invention also relates to a vehicle axle equipped with such an axle crosspiece.
Apart from the provisions set out hereinabove, the invention consists in a certain number of other provisions which will be described more explicitly hereinafter with regard to an exemplary embodiment described with reference to the appended drawing, but which is not in any way limiting.